1. Field of the Invention
This invention relates to a photometric device for use in photographic cameras, and more particularly, to such a device which provides a proper exposure indication under certain variable light conditions.
2. Description of the Prior Art
In recent years, it has been known to use a photo-diode, a photo-transistor, and so forth, having a quick photo-responsive characteristic for a photometric circuit in cameras and the like. When the abovementioned photo-electric conversion element receives light having a light intensity which varies with a frequency twice as high as the frequency of a commercial power source, such as, for example, light from a fluorescent lamp (i.e. 100Hz, 120Hz), the response speed of the element surpasses the abovementioned periodic variation in light intensity with the consequence that an output from the photometric circuit inevitably possesses frequency characteristics of a periodically varying nature. Accordingly, such a difficulty with the known photo-electric conversion element made it inevitable that no accurate indication of proper exposure values could be realized when proper exposure, shutter speed or aperture value to achieve a proper exposure with respect to a light intensity was to be indicated on the basis of an output from the photometric circuit, because these values were also subject to periodic variations.